The chemotherapeutic anthracycline metabolite doxorubicinol (doxOL) has been shown to interact with and disrupt the function of the cardiac ryanodine receptor Ca2+ release channel (RyR2) in the sarcoplasmic reticulum (SR) membrane and the SR Ca2+ binding protein calsequestrin2 (CSQ2). Normal increases in RyR2 activity in response to increasing diastolic SR [Ca2+] are influenced by CSQ2 and are disrupted in arrhythmic conditions. Therefore we explored the action of doxOL on RyR2's response to changes in luminal [Ca2+] seen during diastole...

Developing cardiac myocytes undergo substantial structural and functional changes transforming the mechanism of excitation-contraction coupling from the embryonic form, based on calcium influx through sarcolemmal DHPR calcium channels, to the adult form, relying on local calcium release through RYR calcium channels of sarcoplasmic reticulum stimulated by calcium influx. We characterized day-by-day the postnatal development of the structure of sarcolemma, using techniques of confocal fluorescence microscopy, and the development of the calcium current, measured by the whole-cell patch-clamp in isolated rat ventricular myocytes...

Background: Calcium regulatory proteins-L-type Ca(2+) channels (LTCCs), ryanodine receptor 2 (RyR2), and Na(+)/Ca(2+) exchanger isoform 1 (NCX1) have been recognized as important protective mechanisms during myocardial ischemia-reperfusion injury (I/RI). Both sevoflurane postconditioning (SevoPoC) and delayed remote ischemic preconditioning (DRIPC) have been shown to protect the heart against I/RI. In this study, we aimed to compare the effects of SevoPoC and DRIPC on the expression of the three calcium regulatory proteins in an isolated rat heart model...

Cardiac adaptation to endurance training includes improved contractility by a non-yet clarified mechanism. Since IGF-1 is the main mediator of the physiological response to exercise, we explored its effect on cardiac contractility and the putative involvement of nitric oxide (NO) and CaMKII in control and swim-trained mice. IGF-1 increased cardiomyocyte shortening (128.1±4.6% vs. basal; p˂0.05) and accelerated relaxation (time to 50% relengthening: 49.2±2.0% vs. basal; p˂0.05), effects abrogated by inhibition of: AKT with MK-2206, NO production with the NO synthase (NOS) inhibitor L-NAME and the specific NOS1 inhibitor nitroguanidine (NG), and CaMKII with KN-93...

Aims: The histidine-rich calcium-binding protein (HRC) Ser96Ala variant has previously been identified as a potential biomarker for ventricular arrhythmias and sudden cardiac death in patients with idiopathic dilated cardiomyopathy. Herein, the role of this variant in cardiac pathophysiology is delineated through a novel mouse model, carrying the human mutation in the homologous mouse position. Methods and results: The mouse HRC serine 81, homologous to human HRC serine 96, was mutated to alanine, using knock-in gene targeting...

Ryanodine receptor (RyR) calcium channels are central to striated muscle function and influence signalling in neurones and other cell types. Beneficially low RyR activity and maximum conductance opening may be stabilised when RyRs bind to FK506 binding proteins (FKBPs) and destabilised by FKBP dissociation, with submaximal opening during RyR hyperactivity associated with myopathies and neurological disorders. However this is debated and quantitative evidence is lacking. Here we have measured altered FKBP binding to RyRs and submaximal activity with addition of wild-type (WT) CLIC2, an inhibitory RyR ligand, or its H101Q mutant that hyperactivates RyRs, likely causing cardiac and intellectual abnormalities...

BACKGROUND: Diabetes mellitus is associated an increased risk of ventricular arrhythmias (VA), but the underlying electrophysiological mechanisms are not fully explored. This study was aimed to test whether dynamic factors and Cai handling play roles in arrhythmogenesis of a diabetic animal model. METHODS: We used 26 db/db type 2 diabetes mice and 28 control mice in this study. VA inducibility was evaluated in vivo under isoflurane general anesthesia. The intracellular Ca(2+) (Cai ) and membrane voltage (Vm ) signals of the Langendorff-perfused mouse hearts were simultaneously recorded using the optical mapping technique...

BACKGROUND: Takotsubo syndrome (TTS) is characterized by an acute left ventricular dysfunction and is associated with life-threating complications in the acute phase. The underlying disease mechanism in TTS is still unknown. A genetic basis has been suggested to be involved in the pathogenesis. OBJECTIVES: The aims of the study were to establish an in vitro induced pluripotent stem cell (iPSC) model of TTS, to test the hypothesis of altered β-adrenergic signaling in TTS iPSC-cardiomyocytes (CMs), and to explore whether genetic susceptibility underlies the pathophysiology of TTS...

The mammalian ryanodine receptor Ca(2+) release channel (RyR) has a single conserved high affinity calmodulin (CaM) binding domain. However, the skeletal muscle RyR1 is activated and cardiac muscle RyR2 is inhibited by CaM at submicromolar Ca(2+). This suggests isoform-specific domains are involved in RyR regulation by CaM. To gain insight into the differential regulation of cardiac and skeletal muscle RyRs by CaM, RyR1/RyR2 chimeras and mutants were expressed in HEK293 cells, and their single channel activities were measured using a lipid bilayer method...

Calcium homeostasis is a key factor in the regulation of cardiac excitation-contraction coupling. Calcium dynamics in cardiomyocytes is governed by ATP which depends on insulin dependent glucose concentration, via the glucose transporter type 4 (GLUT4) transporter. It would therefore be interesting to see how calcium dynamics changes in a cardiomyocyte under diabetic conditions. We proposed and analysed a four dimensional ordinary differential equation (ODE) model to capture the interdependency of calcium dynamics on glucose uptake and ATP generation...

INTRODUCTION AND OBJECTIVES: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited disease characterized by polymorphic or bidirectional ventricular arrhythmias (VA) triggered by physical or emotional stress in young people with a structurally normal heart. Beta-blockers are the cornerstone of treatment, while flecainide has recently been incorporated into the therapeutic arsenal. The aim of this study was to report our experience with this drug. METHODS: The cohort included 174 genotype-positive CPVT-patients from 7 families...

Plakophilin-2 (PKP2) is a component of the desmosome and known for its role in cell-cell adhesion. Mutations in human PKP2 associate with a life-threatening arrhythmogenic cardiomyopathy, often of right ventricular predominance. Here, we use a range of state-of-the-art methods and a cardiomyocyte-specific, tamoxifen-activated, PKP2 knockout mouse to demonstrate that in addition to its role in cell adhesion, PKP2 is necessary to maintain transcription of genes that control intracellular calcium cycling. Lack of PKP2 reduces expression of Ryr2 (coding for Ryanodine Receptor 2), Ank2 (coding for Ankyrin-B), Cacna1c (coding for CaV1...

The Cardiomyopathy-associated gene 5 (Cmya5) encodes myospryn, a large tripartite motif (TRIM)-related protein found predominantly in cardiac and skeletal muscle. Cmya5 is an expression biomarker for a number of diseases affecting striated muscle and may also be a schizophrenia risk gene. To further understand the function of myospryn in striated muscle, we searched for additional myospryn paralogs. Here we identify a novel muscle-expressed TRIM-related protein minispryn, encoded by Fsd2, that has extensive sequence similarity with the C-terminus of myospryn...

Increases in the intracellular Ca(2+) concentration in pancreatic islets, resulting from the its mobilization from the intracellular source through the ryanodine receptor, are essential for insulin secretion by glucose. Cyclic ADP-ribose, a potent Ca(2+) mobilizing second messenger synthesized from NAD(+) by CD38, regulates the opening of ryanodine receptor. A novel ryanodine receptor mRNA (the islet-type ryanodine receptor) was found to be generated from the type 2 ryanodine receptor gene by the alternative splicing of exons 4 and 75...

Prolonged action potential duration, reduced action potential firing rate, upstroke velocity and rate of diastolic depolarization have been demonstrated in atrioventricular node (AVN) cells from streptozotocin (STZ)‑induced diabetic rats. To further clarify the molecular basis of these electrical disturbances, the mRNA profiles encoding a variety of proteins associated with the generation and conduction of electrical activity in the AVN, were evaluated in the STZ‑induced diabetic rat heart. Expression of mRNA was measured in AVN biopsies using reverse transcription‑quantitative polymerase chain reaction techniques...